Laminated magnetic coil materials

ABSTRACT

A laminated magnetic material composed of thin rolled sheet of magnetic alloy having a thickness of less than 25 microns and a glassy material formed on at least one surface of the thin rolled sheet of magnetic alloy, wherein the sheet of magnetic alloy and the glassy material are wound and laminated alternately and each of the layers of magnetic alloy is secured to the adjacent layer interposed by an electric insulator.

United States Patent 1191 Tomita 1 March6, 1973 1 LAMINATED MAGNETICCOIL [56] References Cited TERIAL MA S UNITED STATES PATENTS [75]Inventor: Sadami Tomita, Hitachi, Japan 7 3,339,162 8/1967 Bumsteel..l56/184 [73] Assignee: Hitachi, Ltd.,Tokyo,Japan 3,418,710 12/1968Seidel ..29/609 3,468,752 9/1969 Yamamoto ..16l/l96 [221 Flled= Oct 19703,522,108 7/1970 Yamamoto ..117/230 3,528,863 9/1970 Foster ..117/l29[21] Appl' 83532 3,533,861 /1970 Foster ..117 129 [30] ForeignApplication Priority Data Primary Burnett Assistant Examiner--M. E.McCamish Oct. 24, 1969 Japan ..44/847l7 Att0rney Craig, Antonem and i{52] US. Cl. ..336/196, 29/605, 29/609, 57 A T T l61/l96 161/213 336/200336/213, A laminated magnetic material composed of thin I 336/219336/223 rolled sheet of magnetic alloy having a thicknessof [51] intC04) /00 H61f27/30 less than 25 microns and a glassy material formed on[58] Fie'ld "i'gi' 213 56/184 at least one surface of the thin rolledsheet of magnetic alloy, wherein the sheet of magnetic alloy and theglassy material are wound and laminated alternately and each of thelayers of magnetic alloy is secured to the adjacent layer interposed byan electric insulator.

2 Claims, 8 Drawing Figures PATENTEDNAR 61973 ,719,911

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1N VENTOR BY C w g, AWOL, M 5 HKQQ ATTORNEYS LAMINATED MAGNETIC COILMATERIALS BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION Theinvention relates to a magnetic core composed of thin rolled sheet ofhigh permeability magnetic alloy having a thickness of less than 25microns and a method of manufacturing the same. I

2. DESCRIPTION OF THE PRIOR ART There are two types of magnetic coresknown in the art, those which are made of magnetic alloys having a highpermeability such as silicon steel or permalloy, and those which aremade of an oxide magnetic material, namely, ferrite.

With regard to the methods of manufacturing magnetic cores of highpermeability magnetic alloy, a stamped-core method, a toroidalywound-core method and a dust core method are generally known. In themethod of making a stamped-core, a thin sheet of magnetic alloy is firstpunched to form a sheet of desired shape and then a number of punchedsheets are treated for electric insulation and laminated to apredetermined thickness. While in the toroidaly wound-core method, athin sheet of magnetic alloy is wound toroidaly after treatment forelectric insulation. The dust core method is the one, in which powder ofmagnetic alloy is mixed with a binder of an electrically insulatingproperty and then this mixture is molded. On the other hand sintering offerrite is usually applied in a method of forming ferrite cores.-However, magnetic cores formed by pitching powder of magnetic alloy witha binder of an electrically insulating property are not used widely dueto their inferior magnetic properties. Generally, stamped-cores ortoroidaly wound-cores are used with admiration.

However, in practice it has been impossible to form stamped cores ortoroidaly wound-cores employing a sheet of magnetic alloy having athickness of less than 25 microns and therefore, an improvement in thefrequency characteristics in these magnetic cores has been limited. Inother words since a permeability under alternating current conditions isinversely proportional to the square of the thickness of sheettheoretically, the frequency characteristics can be improved by makingthe thickness of the sheet as thiner as possible. The thickness of thesheet which has been employed for making conventional stamped cores ortoroidaly wound-cores, however, has been limited technologicallyresulting in a limitation in the frequency characteristics. The reasonswhy the thickness of the sheet of magnetic alloy has been limited arebased on the following facts: First, stamped cores are manufactured bylaminating a sheet of magnetic alloy after punching by a press machineand applying an electrically insulating treatment. In this punchingwork, the accuracy of punching depends on the ratio of the gap betweenthe male and female patterns and the thickness of the sheet of magneticalloy, and so greater the ratio the higher the accuracy of the work. Infact, punching works'have been performed with relatively good accuracywhere the thickness of the sheet of magnetic alloy is not less than 25microns. However, where the thickness is less than 25 microns the edgeof the punched sheet does not have an acute angle and in addition, sincethe reforming work is difficult technically, this method has beenunpracticable where a thickness of the sheet is less than 25 microns.Secondly, toroidaly wound-cores are manufactured by winding a sheet ofmagnetic alloy spirally, after a treatment for electrical insulation. Inthis method where the sheet of magnetic alloy is too thin, thelamination work is impossible and eventhough the sheet were laminated,the shape of the core thus formed would be deformed. It has beenfoundalso that these defects are produced when the thickness of the sheet ofmagnetic alloy is less than 25 microns.

On the other hand, although those magnetic cores formed by sintering aferrite material present a frequency characteristics of the ferritematerial itself and no influences due to the forming work are observed,ferrite cores have not only such disadvantages that a magnetic fluxdensity is small as compared with high permeability alloys but alsocores themselves are fragile mechanically.

By these reasons mentioned above, if it is possible to form a magneticcore with much thiner sheet of high permeability magnetic alloy thefrequency characteristics of magnetic core would be improved in a greatextent. Furthermore, according to the present technique of rolling work,since it is possible to roll .a sheet of magnetic alloy as thin as 1micron, if it becomes possible to form magnetic cores with such anextremely thin sheet of magnetic alloy an increase in permeability wouldbe far greater.

In conventional stamped cores or toroidaly woundcores, magnesium oxide(MgO) or aluminum oxide (A1 0 is employed as an electric insulator.However, since these kind of electric insulators are not adhesive andthey are not secured between the laminated layers, these insulators aresubjected to be broken away from the layers in time. Therefore, if it ispossible to make an electric insulator to be secured to the sheet ofmagnetic alloy in such laminated condition, then a magnetic core of highreliability would be realized.

SUMMARY OF THE INVENTION A primary object of the present invention is toprovide a laminated magnetic material composed of extremely thin sheetof high permeability magnetic alloy.

A further object of this invention is to provide a laminated magneticmaterial in which a high permeability magnetic alloy and an electricinsulator are laminated securely and are formed in a desired shape.

A still further object of this invention is to provide a laminatedmagnetic material provided with coils.

A still further object of this invention is to provide a laminatedmagnetic material on which a plurality of elements, such as a pluralityof cores or magnetic heads, are formed.

A still further object of this invention is to provide a method ofmanufacturing a laminated magnetic material composed of very thin sheetof high permeability magnetic alloy. i 1

A still further object of this invention is to provide method ofmanufacturing laminated magnetic material provided. with coils.

This invention relates to a laminated magnetic material composed of verythin sheet of high permeability magnetic alloy and a method of makingthe same.

The laminated magnetic material according to the present invention ischaracterized in that it is composed of substantially very thin sheet ofmagnetic alloy with high permeability wound spirally, and that a glassymaterial is formed interposing between the layers of magnetic alloy, theglassy material being adhered to the adjacent sheet of magnetic alloy.

In such a structure, the glassy material does not break away and even anextremely thin magnetic alloy can be formed into a toroidaly wound-core.

In order to improve a permeability of the laminated magnetic materialwhich is used for A.C. equipment, the thiner the sheet of magneticmaterial the better.

Although it has been impossible to press or to wind the sheet ofmagnetic alloy having a thickness less than 25 microns, by applying aparticular method according to this invention it has become possible tomanufacture a laminated magnetic material of such a structure describedabove.

The method according to this invention is such that a glassy film isformed on the sheet of high permeability magnetic alloy, and the sheetof magnetic alloy is wound and laminated around a support base ofnonmagnetic material so that the sheet of magnetic alloy and the glassyfilm are laminated alternately, and then the laminated body is heated toa temperature higher than the softening point of the glassy material soas to make the layers of the laminated body fused and united. In thismethod, even with a very thin sheet of magnetic material any deformationof the thin sheet is effectively prevented.

The glassy material employed in this invention for electric insulationprovides a good adhesive property advantageously as compared tomagnesium oxide or aluminum oxide. This glassy'material may be formed bya high frequency sputtering. technique easily. In such cases where theglassy material formed on the sheet of magnetic alloy contains bubblesin itself, it is apt to be broken away from the sheet of magnetic alloyresulting in .a deterioration of the electrical characteristics.Therefore, it is preferable to heat the laminated body after forming theglassy film to a temperature higher than the softening point of theglassy material and to remove the bubbles from the glassy material.

On the other hand, where work strains are caused in the magnetic alloydue'to the works such as rolling work, the permeability decreases in agreat extent. For this reason annealing is usually applied after thework so as to remove the work strain. This annealing is generallyperformed by heating after laminating the sheet of magnetic alloy andthe electric insulator alternately, to a temperature higher than therecrystallization point of the magnetic alloy and then by coolin it in afurnace.

Therefore, where the glassy material has a softening point lower thanthe annealing temperature, the glassy material might be fell-out fromthe layer between the layers of magnetic material. Itis desirable,therefore, to use such a-glassy material which is softened at theannealing temperature and further to softening treatment simultaneouslywith the annealing treatment. By applying the both softening andannealing treatments simultaneously, another advantageous effect may beobtained, in which, where the sheet of magnetic material is covered witha glassy material only on one surface thereof, the glassy material isnot adhered to the other surface of the sheet and no adhesive action iseffected thereto. However, upon applying the annealing treatment, sincethe glassy material is subjected to be softened at the same time, theglassy material is fused to the other surface of the sheet of magneticmaterial on which surface the glassy material was not depositedoriginally. As a result, a laminated magnetic material is formed witheach layer securely adhered to the other. In such case, where a glassymaterial is formed on both surfaces of the sheet, before applying anannealing treatment each glassy film on one sheet of magnetic materialis not adhered to the adjacent glassy film of the other sheet, howeverthese two glassy films can be fused and adhered in the process ofannealing treatment.

In order to increase a adhesiveness of the glassy material, it ispreferable to form a film of oxide preliminary over the surface of themagnetic alloy. This film of oxide favorably improves the electricinsulation of the glassy material. The formation of the film of oxidemay be carried out by heating the magnetic alloy in the atmosphere ofoxygen.

It will be readily convinced that the laminated magnetic materialhereinbefore mentioned has a remarkable frequency characteristics due tothe fact that the thickness of the sheet of magnetic material has beenreduced in a great extent. Further, for the purpose of utilizing thelaminated magnetic material as a part of some electrical equipment, itis desirable that the laminated magnetic material thus formed isprovided with a coil wound thereof. Accordingly it is very useful tomanufacturesuch laminated magnetic material. A method according to thisinvention is directed to eliminate the process of winding coilconductors around the laminated magnetic material. Furthermore, it is sodesigned as to utilize the nonmagnetic support base which is used onlyin a process of lamination to reinforce the mechanical strength of thelaminated magnetic material. To achieve these requirements, in thepresent invention predetermined number of coil conductors are disposedon the surface of the support base of non-magnetic material along thelongitudinal direction ofthe support base insulated electrically fromthe base with an insulator, and outside these coil conductors sheet ofhigh permeability magnetic alloy and glassy film are wound alternatelyone after the other thus forming a lamination, and following thisprocess outside this laminated magnetic material the same number of coilconductors as those disposed before are disposed longitudinallyinsulated electrically from the sheet of magnetic material, and thencoil conductors disposed inside and outside the laminated magneticmaterial are bridged so as to allow a current to flow through the coilconductors successively. Thus, the coil winding process, which isperformed after the laminating process and is a troublesome work hasbeen eliminated according to this invention. Any material having a highelectrical conductivity, for example a copper, is suitable for coilconductors. These coil can be deposited on the nonmagnetic support baseby means of evaporation, in which a masking plate may be used to definethe intended portions on which the evaporation is not applied. In suchinstances where the support base is made of an electrically conductivematerial, it is necessary to form an electric insulating film over thesurface of the nonmagnetic support base for the purpose of providingelectrical insulation between any two of the coil conductors. Since thisinsulating film is not subjected to be wound as is the case with theglassy material formed on the sheet of magnetic alloy, a highcohesiveness is not required, therefore any suitable material other thanglassy material may be employed.

The coil conductors disposed on the support base are also insulatedelectrically from the sheet of magnetic alloy, accordingly, where theglassy material formed thereon is facing the coil conductors, the glassyfilm may be utilized as an electric insulator therebetween. However,where the glassy material is not so formed as to face the coilconductors, an electric insulator must be formed on the coil conductors.

In order to perform the bridging work for the coil conductors disposedinner and outer surfaces of the laminated magnetic alloy, suchparticular designing considerations with respect to the direction of thecoil conductors to be disposed are desirable. For example, where thepredetermined number of coil conductors are disposed on both inner andouter surfaces of the cylindrical support base of non-magnetic materialalong the axis of the support base, the coil conductors disposed on theouter surface of the cylindrical support base are arranged in such amanner that each of the outer coil conductors is extended from one endof the corresponding inner conductor to the other end of the adjacentinner conductor, in other words the outer coil conductors are skewedalong the axis of the cylindrical support base by one pitch, or theinterval of the conductors.

It is also necessary that where the outer and inner coil conductors areto be bridged, both end surfaces of the cylindrically shaped laminatedmagnetic material must be covered with an electric insulator, otherwisea current would flow through the bridge to the laminated magneticmaterial resulting in a malfunction of the magnetic core. The electricinsulator for this purpose may be obtained by depositing a conventionalelectric insulator film, for example by a high frequency sputteringtechnique.

The bridging of the both outer and inner coil conductors are carried outeasily by an evaporation technique in the same way as the forming of thecoil conductors, or instead of this way soldering of a conductor stripto both ends of the coil conductors may also be applied.

When the laminated magnetic material thus formed is applied formulti-elements purpose, the processes for mounting a plurality ofelements on the laminated magnetic material would be eliminated andconsequently the structure of the manufactures would be much simplified.These requirements are also satisfied in this invention by utilizing thenommagnetic support base effectively. For this purpose, the laminatedmaterial and coil conductors are grooved together circumferentialy sothat the bottom of the groove reaches at the electric insulator filmdeposited on the surface of the non-magnetic support base. The numberand the width of the grooves are arbitrary selected according to thenumber of the elements required. Following to the forming of the groovesbridging of the outer and inner coil conductors are naturally carriedout.

Among magnetic alloys, permalloy are more suitable than silicon-steelfor such a purpose where an excellent frequency characteristics isrequired, because the former has a higher permeability than the latter.

The laminated magnetic material according to this invention are usedadvantageously for cores or cores with coils to be used in various partsand equipments. In addition, it is also applicable for magneticrecording heads by forming an air gap on the portion of the laminatedmagnetic material.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross sectional viewillustrating a structure of a laminated magnetic material in which asheet of high permeability magnetic alloy having a glassy film depositedon the surface thereof is wound around a support base of non-magneticmaterial.

FIG. 2 is a perspective view which shows a disposition of coilconductors on a support base of nonmagnetic material.

FIG. 3 is a cross-sectional view which shows coil conductors disposed onboth outer and inner surfaces of a laminated magnetic material.

FIG. 4 shows the section IV of FIG. 3 in detail.

FIG. 5 is a perspective view which illustrates a bridging of outer andinner coil conductors.

FIG. 6 is a graph illustrating a variation in an effective permeabilitywith frequency.

FIG. 7 is a perspective view illustrating a formation of amulti-elements magnetic recording heads.

FIG. 8 shows a ring of glassy material which is employed for bridgingcoil conductors, which conductors are disposed on outer and innersurfaces of a laminated magnetic material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 The presentinvention is primarily directed to provide a laminated magnetic materialwith excellent frequency characteristics. Accordingly, a rolled sheet ofl 1 weight Fe-83 weight Ni-6 weight V alloy, having a thickness of 10microns was employed as a sheet of high permeability magnetic alloy.This sheet of magnetic alloy was covered with a glassy film at first andthen it was laminated on a support base of nonmagnetic material. Thesheet of Fe-Ni-V alloy was 20 mm in width and 410 mm in length. Amixture of magnesium fluoride (MgF,) and glass of low melting point withsoftening point of about 550C was selected for a glassy material. 7

Prior to the forming of a glassy film, the surface of Fe Ni-V alloy wascleaned by applying a pickling treatment, and then it was heated in theatmosphere of oxygen in order to form a thin film of oxide on thesurface of the alloy. Following to these processes, a mixture ofmagnesium fluoride and low-melting point glass was deposited on onesurface of the sheet of Fe-Ni-V alloy to a thickness of about 2 micronsby high frequency sputtering. The sheet of Fe-Ni-V alloy was then woundaround a stainless steel tube in such a manner that the glassy filmalways appears outside during the winding process. The tube of stainlesssteel (SUS 52) was 13 mm in outer diameter, 11 mm in inner diameter and30 mm in length and the surface thereof was smoothed. The number oflayers formed by the laminated sheet of Fe-Ni-V alloy was ten and theremnant of the sheet was cut and removed. In this case, the innersurface of the stainless steel tube had been screwed beforehand in orderto remove the tube by pulling out of the laminated magnetic materialeasily after completion of the lamination process.

Following the winding process, it was heated to a temperature higherthan the softening point of the glassy material, for example to atemperature of about 700C. Due to this heat treatment the glassymaterial was melted and fused to the adjacent sheet of Fe-Ni-V alloysecurely and consequently the laminated magnetic material united solidlywas formed. FIG. 1 shows the laminated magnetic material formed asbefore indicated and numeral 1 represents a stainless steel tube, 2 is asheetof Fe-Ni-V alloy and 3 is a glassy film. After the laminatingprocess the stainless steel tube was removed from the laminated magneticmaterial by pulling the shaft which had been screwed in the tube. Thelaminated magnetic material had no indication of deformation and it wasformed in the cylindrical shape with uniform inner diameter along itsaxis. The laminated magnetic material composed of the sheet of highpermeability magnetic alloy which sheet having a thickness of less than25 microns was thus realized, and since the electric insulator film isfirmly secured to the sheet of magnetic alloy in this invention, a goodelectric insulation properties as well as a long life have been achievedsuccessfully.

Embodiment 2 It is indeed very desirable for applying a laminatedmagnetic material to some parts and equipments in practical use, if coilconductors are provided on the laminated magnetic material. In thisembodiment, the stainless steel tube 1 was not removed but it wasutilized for disposing coil conductors on the tube, because the tuberemained unremoved was not harmful for practical use, but on thecontrary it was useful in some cases to improve a mechanical strength.In this embodiment, the dimensions of the tube 1 was the same asEmbodiment 1. Prior to the disposition of coil conductors, silicon oxide(SiO was deposited on the surface of the tube by high frequencysputtering to a thickness of 2 microns so as to provide an electricinsulator between the tube 1 and coil conductors. To obtain an insulatorfilm of uniform thickness the tube was rotated at a constant'speed ontheaxis by driving a shaft screwed in the tube. Then, coil conductors weredeposited on the surface of the stainless tube 1 along the axis. Thecoil conductors deposited by vacuum evaporation were ten conductors withequal intervals, and each conductor was so designed as to have athickness of 3 microns and a width of 1.5 mm. Accordingly, the portionson which the evaporation was not intended to be applied were coveredwith a masking plate. The vacuum evaporation was carried out by a highfrequency heating technique in a vacuum of 1X10" mm Hg, and anevaporation temperature was at about l,500C.

Following to the deposition of the coil conductors by evaporation, afilm of silicon oxide was formed over the whole surface by highfrequency sputtering. FIG. 2 shows coil conductors deposited on thesurface of the stainless steel tube 1, and numeral 4 represents a coilconductor, 5 is a film of silicon oxide formed on the surface of thestainless steel tube 1, and 6 is a film of silicon oxide formed on thecoil conductor 4 after completion of the deposition of the coilconductors.

For a high permeability magnetic alloy material to be used, a sheet of11 weight Fe-83 weight Ni-6 weight V alloy with a thickness of 10microns was employed. AT first, a thin film of oxide was formed on thesheet of magnetic alloy and then a glassy material which is a mixture ofmagnesium fluoride and low melting point glass with softening point ofabout 550C was formed to a thickness of 2 microns by a high frequencysputtering technique. The width and length of the sheet of Fe-Ni-V alloywas the same as embodiment l. The sheet of composite magnetic materialformed as described before was wound around the stainless tube 1. Thenumber of layers was 10. Upon completion of the winding process, it washeated to a temperature of about 700C, and each glassy material wasfused and secured to the adjacent glassy material. Since therecrystallization temperature of the Fe-Ni-V alloy is about 600C, anannealing was also progressed together with the softening of the glassymaterial. Silicon oxide was then deposited on the surface of thelaminated magnetic material to a thickness of 2 microns and further thecoil conductors were evaporated thereon to a thickness of 3 microns, andin addition silicon oxide was deposited further thereon. Thesedeposition processes are the same as those in which silicon oxides 5 and6 were deposited on the stainless tube 1 and the coil conductors 4 wasdeposited by evaporation. The coil conductors were disposed so that eachconductor extends from one end of the corresponding inner coil conductor4 to the other coil conductor end of the adjacent inner coil conductor.FIG. 3 shows a cross section of the laminated magnetic material providedwith coil conductors, those members 1 to 6 are explained referring toFIGS. 1 and 2, and in which numeral 7 designates a coil conductordisposed on the laminated magnetic material, 8 is a film of siliconoxide formed between the laminated magnetic material and coilconductors, and 9 is a film of silicon oxide formed over the coilconductor 7. FIG. 4 shows an expanded section A of FIG. 3 andillustrates a construction in detail.

After completion of the disposition of coil conductors 4 and 7 on bothsurfaces of the laminated magnetic material, both end surfaces of thelaminated magnetic material was covered with silicon oxide to athickness of 5 microns by a high frequency sputtering technique, andthen both corresponding conductor ends of coil conductors 4 and 7 werebridged by evaporating a copper so as to complete a coil winding.

FIG. 5 shows a connection by bridging outer coil conductor 7 and innercoil conductor 4, in which 10 is a film of silicon oxide formed on theend surface of the laminated magnetic material, and 11 is a copper foilevaporated.

Table 1 illustrates a D.C. magnetizing characteristics of the laminatedmagnetic material manufactured according to this invention. A D.C.magnetizing characteristics is not influenced by a thickness of thesheet of magnetic alloy, but substantially effected by a composition ofmaterials of the core as well as manufacturing processes. Table 1 showsin what degree the magnetic core made oflaminated magnetic superior inD.C. magnetizing characteristics to the ferrite cores and dust cores.

The ferrite core was made by sintering Mn-Zn ferrite (a composite ofMnO, ZnO, and Fe o in the shape of ring of inner diameter of 12 mm,outer diameter of IS mm, and a hight of 3 mm, while the dust core wasmade by molding a powder of 11 weight Fe-83 weight Ni-6 weight% V alloywith a binder in the shape of ring of the same size as the ferrite corementioned above.

Where, B is a flux density when a magnetic field intensity H is 10oersteds B is a flux density when a magnetic field intensity H is loersted, Br is a remanent flux density, l-lc is a coercive force, ;:.0is a initial permeability, and pm is a maximum permeability.

For magnetic cores with suitable properties, magnetic flux density andpermeability are required to be great, whereas a coercive force must besmall. The laminated magnetic material of Fe-Ni-V alloy is superior tothe both ferrite cores and dust core in view of the required properties.

FIG. 6 shows a variation in effective permeability of laminated magneticmaterials with frequency. In which 100p. and 50p. represent cores madeof the sheets having a thickness of 100 microns and 50 micronsrespectively. These two cores are formed at first by punching a rolledsheet of 1 1 weight Fe-83 weight Ni-6 weight V alloy in the shape ofring of an outer diameter of 35 mm, inner diameter of 25 mm, and then bylaminating to five layers interposing an electric insulator between thelayers of magnetic alloy.

Generally a permeability of magnetic core tends to decrease with higherfrequency. Therefore, if such a core, which has a high frequency and thepermeability does not decrease with respect to the frequency increase,is achieved it would be obvious that the core provides an excellentproperties. The magnetic core made of laminated magnetic materialaccording to this invention was proved to be the one which meets thoserequirements completely.

Embodiment 3 For the purpose of applying the laminated magnetic materialin embodiment 2 to a magnetic head for a magnetic tape with twentytracks, a groove 12 was formed circumferentially as deep as the bottomof the groove reaches at the silicon oxide film formed on the stainlesssteel tube 1 as shown in FIG. 7, and a gap 13 was made on the portionwhere no coil conductors were deposited. The width of the track 14 andthe interval of tracks (or the width of the groove) were 0.5 mm. Thesecutting works and machine works were carried out by means of electronbeam.

Prior to the connection of the outer and inner coil conductors 4i and 7of each track for making a complete coil winding, end surfaces of thelaminated magnetic material exposed by the grooving were covered withsilicon oxide to a thickness of 5 microns by a high frequency sputteringtechnique.

Then a glass plate 15 having a number of copper foils 16 evaporated onboth surfaces thereof and which glass plate being formed in the shape ofring divided into two parts as shown in FIG. 8, was inserted into thegrooved portion. The glass plate 15 is made of borosilicate glass havinga softening point of about 750C, and its shape is formed as the innersurface fits the bottom surface of the groove 12. On both end surfacesof the glass plate 15, a number of copper foils 16 is evaporated to athickness of 5 microns in such a manner that the copper foils bridge theouter and inner coil conductors 4 and 7 of the track 141 and completesthe coil winding upon inserting the glass plate into the groove 12. Thewidth of the glass plate 14 including the thickness of the copper foil16 was selected to be 0.40 mm.

After inserting the glass plate 15 into the groove 12, the coilconductors 4 and 7 were connected to the evaporated copper foil 16respectively with Sn-Pb solder.

With respect to the magnetic head manufactured as describedhereinbefore, a dielectric strength of coil, an allowable current ofcoil, and magnetic characteristics at the frequency of 100 KH weremeasured, those results of the measurement are shown in Table 2.

TABLE 2 Dielectric strength of coil About 80V Allowable current of coilAbout 60 mA Total magnetic flux 2.4 maxwell (coil current is 60 mA)Rectangular ratio 64% Coercive force 0.08 0e Effective permeability6,500

(coil current I0 mA) Various characteristics shown in Table 2 wereproved to be entirely sufficient for magnetic head for practical use.

Further, since the effective permeability at the frequency of 100 KH ofa stamped core formed by laminating a rolled sheet of ll weight l e-83weight Ni-6 weight V alloy (a thickness of 100 microns) together with anelectric insulator film were about 800,

it was proved that the effective permeability of the core electricinsulator.

2. A laminated magnetic material having a coil according to claim 1wherein said wound and laminated body and said coil conductors disposedon the outer and inner surfaces of said wound and laminated body aredivided by a groove crossing said coil conductors to form dividedsections, and

a plurality of copper foils are disposed on each end surface of saiddivided sections exposed by said groove and said copper foils formbridge connections between said outer and inner coil conductors.

1. A laminated magnetic material having a coil comprising, anon-magnetic support base, an electric insulator film formed on thesurface of said support base, a plurality of inner coil conductorsdisposed on said insulator film along the longitudinal direction of saidsupport base, a rolled sheet of high permeability magnetic alloy, saidsheet of magnetic alloy having a thickness of less than 25 microns, aglassy material formed on at least one surface of said sheet of magneticalloy, said sheet of magnetic alloy and said glassy material being woundand laminated alternately and crossing said inner coil conductors, aplurality of outer coil conductors disposed on an electric insulatorfilm forced on said wound and laminated body, and a plurality ofconductor foils bridging said outer and inner coil conductors disposedon both outer and inner surfaces of said laminated body, wherein eachlayer of said wound and laminated body is secured to the adjecent layerand interposed by an electric insulator.